The diagnostic category of amnesia associated with mild cognitive impairment (MCI) attempts to describe those people who have memory loss but relatively preserved abilities in other cognitive areas so as not to merit a diagnosis of dementia. The importance of this group of people is that they represent a population at high risk of developing dementia, especially Alzheimer's disease, and are an appropriate target for early diagnosis and intervention strategies. Accordingly, the major goal of this proposal is to determine whether sensitive behavioral tasks together with eye-tracking technology will reveal a profile of performance in MCI patients that is useful in predicting the onset of Alzheimer's Disease or other dementias. The overall plan is to test a minimum of 60 MCI patients and 60 matched normal control (NC) subjects (recruited from the Clinical Core) initially and on yearly follow-up sessions on two declarative memory tasks and one nondeclarative memory task, together with eye-tracking. We have good experience with all of the tasks and with eye-tracking, and we have successfully administered the preferential looking task together with eye-tracking in pilot work with MCI, PD, and NC subjects. A group of 30 patients with Alzheimer's Disease (AD) and a group of 30 Parkinson's Disease patients without dementia (PD) also will be tested (these groups will also be recruited from the Clinical Core). The performance of the AD and PD groups and the NC group will provide important points of comparison with the performance of the MCI patients initially and at follow-up sessions. The PD group also serves as a critical control group for the MCI and AD patients. Specifically, PD patients, like the AD patients, have neurologic damage, but unlike AD patients, the PD patients don't have dementia. An important contribution from this work would be the ability to diagnose sooner than is now possible in MCI patients oncoming cognitive decline, at a time when the nervous system is less compromised and, accordingly, more likely to benefit from therapeutic intervention.